U.S. patent number 5,847,479 [Application Number 08/839,724] was granted by the patent office on 1998-12-08 for self-pressure-balanced hydrodynamic bearing spindle motor.
This patent grant is currently assigned to SAE Magnetics (H.K.) Ltd.. Invention is credited to Charles J. Cheever, Frank A. Gray, Leoi Sun, Jian M. Wang.
United States Patent |
5,847,479 |
Wang , et al. |
December 8, 1998 |
Self-pressure-balanced hydrodynamic bearing spindle motor
Abstract
A hydrodynamic spindle motor of the present invention may
include a shaft having a thrust bearing plate, an insert
surrounding the shaft above the thrust bearing plate, and a sleeve
surrounding the shaft below the thrust bearing plate. In one
embodiment the thrust bearing plate is substantially centrally
positioned along the longitudinal axis of the shaft. Preferably
either the shaft has annular skewed herringbone shaft grooves or,
alternatively, the insert has annular skewed herringbone insert
grooves and the sleeve has annular skewed herringbone sleeve
grooves. A set of circulation channels above the thrust bearing
plate and a set of circulation channels below the thrust bearing
plate preferably cross a shaft bore to allow for flow of
lubricating fluid. A face seal may be formed between the lower
radial cap surface of an end cap and an upper radial insert surface
of the insert. The face seal may be used to form a capillary seal
when the motor is in a static state and a pumping seal when the
motor is in a dynamic state. The face pattern, in one embodiment,
has a first annular zone adjacent the shaft, a middle annular
groove, and a second annular zone.
Inventors: |
Wang; Jian M. (Tigard, OR),
Sun; Leoi (Tigard, OR), Cheever; Charles J. (Beaverton,
OR), Gray; Frank A. (Portland, OR) |
Assignee: |
SAE Magnetics (H.K.) Ltd. (San
Jose, CA)
|
Family
ID: |
25280490 |
Appl.
No.: |
08/839,724 |
Filed: |
April 15, 1997 |
Current U.S.
Class: |
310/90; 384/107;
384/112; G9B/19.029 |
Current CPC
Class: |
F16C
33/107 (20130101); H02K 5/1677 (20130101); F16C
17/107 (20130101); G11B 19/2018 (20130101); F16C
2370/12 (20130101) |
Current International
Class: |
F16C
33/04 (20060101); G11B 19/20 (20060101); F16C
33/10 (20060101); H02K 5/16 (20060101); H02K
005/16 (); F16C 032/06 () |
Field of
Search: |
;310/67R,90,90.5
;384/100,107,112,113,123,132,133 ;360/98.07,99.04,99.08
;277/399,400 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"Development of Non-Contacting, Non-Leaking Spiral Groove Liquid
Face Seals", by Tom Lai, Presented as a Society of Tribologists and
Lubrication Engineers paper, STLE/ASME Tribology Conference, New
Orleans, Louisiana, Oct. 24-27, 1993, Lubrication Engineering, vol.
50, 8, pp. 625-627, 629..
|
Primary Examiner: LaBalle; Clayton
Attorney, Agent or Firm: Chernoff, Vilhauer, McClung &
Stenzel, LLP
Claims
We claim:
1. A spindle motor having hydrodynamic bearings, said motor
comprising:
(a) a shaft having a radial thrust bearing plate substantially
perpendicular to said shaft, said thrust bearing plate having upper
and lower radial plate surfaces, said shaft having a shaft outer
diameter and a longitudinal axis;
(b) an insert having an insert inner diameter and a lower radial
insert surface substantially perpendicular to said insert inner
diameter, said insert inner diameter surrounding said shaft outer
diameter above said thrust bearing plate to form an upper axial
cavity therebetween, said lower radial insert surface being at
least partially coextensive with said upper radial plate
surface;
(c) a sleeve having a sleeve inner diameter and a radial sleeve
support surface substantially perpendicular to said sleeve inner
diameter, said sleeve inner diameter surrounding said shaft outer
diameter below said thrust bearing plate to form a lower axial
cavity therebetween, said radial sleeve support surface being at
least partially coextensive with said lower radial plate
surface;
(d) said insert positioned within said sleeve; and
(e) said thrust bearing plate being substantially centrally
positioned along said longitudinal axis of said shaft.
2. The motor of claim 1, said shaft outer diameter having shaft
grooves.
3. The motor of claim 1 wherein said shaft grooves have a
herringbone pattern with a central point, said central point being
skewed off-center.
4. The motor of claim 3 wherein said central point is skewed
off-center toward said thrust bearing plate.
5. The motor of claim 1, said insert inner diameter having insert
grooves and said sleeve inner diameter having sleeve grooves.
6. The motor of claim 1 wherein said insert grooves and sleeve
grooves have a herringbone pattern with a central point, said
central point being skewed off-center.
7. The motor of claim 6 wherein said central point is skewed
off-center toward said thrust bearing plate.
8. The motor of claim 1, said upper and lower radial plate surfaces
having an annular herringbone pattern with an annular central
point, said annular central point being skewed off-center.
9. The motor of claim 8 wherein said annular central point is
skewed off-center annularly away from said shaft.
10. The motor of claim 1, said lower radial insert surface and said
radial sleeve support surface having an annular herringbone pattern
with an annular central point, said annular central point being
skewed off-center.
11. The motor of claim 10 wherein said annular central point is
skewed off-center annularly away from said shaft.
12. The motor of claim 1, said shaft having a first set of
circulation channels located above said thrust bearing plate and a
second set of circulation channels located below said thrust
bearing plate.
13. The motor of claim 12 wherein both said first set of
circulation channels and said second set of circulation channels
cross a shaft bore.
14. The motor of claim 1 further comprising:
(a) a first set of circulation channels in said shaft positioned
above said thrust bearing plate; and
(b) a second set of circulation channels in said shaft positioned
below said thrust bearing plate;
(c) wherein said circulation channels and said shaft bore together
allow lubricating fluid to flow in a first direction down from
above said thrust bearing plate to below said thrust bearing plate
and to flow in a second direction up from below said thrust bearing
plate to above said thrust bearing plate.
15. The motor of claim 1 further comprising:
(a) said insert having an upper radial insert surface; and
(b) a compensation slot formed in said insert inner diameter below
said upper radial insert surface.
16. The motor of claim 15 further comprising at least one access
channel between said compensation slot and said upper radial insert
surface.
17. The motor of claim 1 further comprising:
(a) said insert having an upper radial insert surface;
(b) an end cap having a lower radial cap surface at least partially
coextensive with said upper radial insert surface; and
(c) a face seal formed between said lower radial cap surface and
said upper radial insert surface.
18. The motor of claim 17 wherein said lower radial cap surface has
a face pattern, said face pattern having raised surfaces and
lowered surfaces.
19. The motor of claim 18 wherein said raised surfaces are parallel
to said upper radial insert surface, said raised surfaces and said
upper radial insert surface defining a capillary cavity
therebetween.
20. The motor of claim 17 wherein said lower radial cap surface has
a face pattern, said face pattern having a first annular zone
adjacent said shaft, a middle annular groove, and a second annular
zone.
21. The motor of claim 17 wherein said upper radial insert surface
has a face pattern, said face pattern having raised surfaces and
lowered surfaces.
22. The motor of claim 21 wherein said raised surfaces are parallel
to said lower radial cap surface, said raised surfaces and said
lower radial cap surface defining a capillary cavity
therebetween.
23. The motor of claim 17 wherein said upper radial insert surface
has a face pattern, said face pattern having a first annular zone
adjacent said shaft, a middle annular groove, and a second annular
zone.
24. The motor of claim 1 further comprising:
(a) an annular end cap having a lower radial cap surface and a cap
outer diameter;
(b) said insert having an insert outer diameter and an upper radial
insert surface, said upper radial insert surface at least partially
coextensive with said lower radial cap surface;
(c) said sleeve having an upper sleeve inner diameter surrounding
said cap outer diameter and said insert outer diameter; and
(d) an annular z-slot formed below said lower radial cap surface
and between said sleeve inner diameter and said insert outer
diameter.
25. A spindle motor having hydrodynamic bearings surrounding a
shaft, said motor comprising:
(a) a thrust bearing plate perpendicular to said shaft;
(b) a first set of circulation channels in said shaft, said first
set of circulation channels positioned above said thrust bearing
plate;
(c) a second set of circulation channels in said shaft, said second
set of circulation channels positioned below said thrust bearing
plate;
(d) a shaft bore in said shaft; and
(e) both said first set of circulation channels and said second set
of circulation channels crossing said shaft bore;
(f) wherein said circulation channels and said shaft bore together
allow flow of lubricating fluid.
26. The motor of claim 25 wherein said circulation channels and
said shaft bore together allow lubricating fluid to flow in a first
direction down from above said thrust bearing plate to below said
thrust bearing plate and to flow in a second direction up from
below said thrust bearing plate to above said thrust bearing
plate.
27. The motor of claim 25 wherein said flow is determined by
pressure surrounding said shaft.
28. A spindle motor having hydrodynamic bearings, said motor
comprising:
(a) a shaft having a longitudinal axis;
(b) a radial thrust bearing plate perpendicular to said shaft and
centrally positioned on said longitudinal axis of said shaft;
(c) an annular insert surrounding said shaft above said thrust
bearing plate and an annular sleeve surrounding said shaft below
said thrust bearing plate;
(d) an upper axial cavity formed between said shaft and said
annular insert and a lower axial cavity formed between said shaft
and said annular sleeve;
(e) a first set of circulation channels in said shaft positioned
above said thrust bearing plate and a second set of circulation
channels in said shaft positioned below said thrust bearing
plate;
(f) a shaft bore in said shaft, both said first set of circulation
channels and said second set of circulation channels crossing said
shaft bore; and
(g) an annular compensation slot formed in said insert and
surrounding said shaft;
(h) wherein said circulation channels, said shaft bore, and said
compensation slot together allow lubricating fluid to flow between
said upper axial cavity and said lower axial cavity.
29. A spindle motor having hydrodynamic bearings, said motor
comprising:
(a) a shaft having a longitudinal axis;
(b) a first radial surface substantially perpendicular to said
shaft;
(c) a second radial surface substantially perpendicular to said
shaft;
(d) said first radial surface at least partially coextensive to
said second radial surface; and
(e) a face seal formed between said first radial surface and said
second radial surface, said face seal being a capillary seal when
said motor is in a static state.
30. The motor of claim 29 wherein said first radial surface has a
face pattern, said face pattern having raised surfaces and lowered
surfaces.
31. The motor of claim 30 wherein said raised surfaces are parallel
to said second radial surface, said raised surfaces and said second
radial surface defining a capillary cavity therebetween.
32. The motor of claim 30 wherein said raised surfaces are in a
swirl pattern.
33. The motor of claim 29 wherein said first radial surface has a
face pattern, said face pattern having a first annular zone
adjacent said shaft, a middle annular groove, and a second annular
zone.
34. The motor of claim 33 wherein said first annular zone has
raised surfaces that swirl from a first position adjacent to said
shaft to a second position less than 140 degrees from said first
position and adjacent said middle annular groove.
35. The motor of claim 29 wherein said face seal is a pumping seal
when said motor is in a dynamic state.
36. A spindle motor having hydrodynamic bearings, said motor
comprising:
(a) a shaft having a radial thrust bearing plate substantially
perpendicular to said shaft, said thrust bearing plate having upper
and lower radial plate surfaces, said shaft having a shaft outer
diameter and a longitudinal axis;
(b) an insert having an insert inner diameter and a lower radial
insert surface substantially perpendicular to said insert inner
diameter, said insert inner diameter surrounding said shaft outer
diameter above said thrust bearing plate to form an upper axial
cavity therebetween, said lower radial insert surface being at
least partially coextensive with said upper radial plate
surface;
(c) a sleeve having a sleeve inner diameter and a radial sleeve
support surface substantially perpendicular to said sleeve inner
diameter, said sleeve inner diameter surrounding said shaft outer
diameter below said thrust bearing plate to form a lower axial
cavity therebetween, said radial sleeve support surface being at
least partially coextensive with said lower radial plate
surface;
(d) said thrust bearing plate being substantially centrally
positioned along said longitudinal axis of said shaft;
(e) an annular end cap having a lower radial cap surface and a cap
outer diameter;
(f) said insert having an insert outer diameter and an upper radial
insert surface, said upper radial insert surface at least partially
coextensive with said lower radial cap surface;
(g) said sleeve having an upper sleeve inner diameter surrounding
said cap outer diameter and said insert outer diameter; and
(h) an annular z-slot formed below said lower radial cap surface
and between said sleeve inner diameter and said insert outer
diameter.
37. The motor of claim 25 wherein said first and second sets of
circulation channels are crossing sets of circulation channels.
38. A method for constructing a spindle motor having hydrodynamic
bearings and a shaft with a centrally located radial thrust bearing
plate, said method comprising the steps of:
(a) positioning a sleeve within a motor, said sleeve having a
sleeve inner diameter and a radial sleeve support surface
substantially perpendicular to said sleeve inner diameter;
(b) inserting a shaft into said sleeve, said shaft having a radial
thrust bearing plate substantially perpendicular to said shaft,
said thrust bearing plate having upper and lower radial plate
surfaces, said shaft having a shaft outer diameter and a
longitudinal axis, said thrust bearing plate being substantially
centrally positioned along said longitudinal axis of said
shaft;
(c) forming a lower axial cavity between said sleeve inner diameter
and said shaft outer diameter below said thrust bearing plate;
(d) positioning an annular insert within said sleeve and around
said shaft, said insert having an insert inner diameter and a lower
radial insert surface substantially perpendicular to said insert
inner diameter, said lower radial insert surface being at least
partially coextensive with said upper radial plate surface;
(e) forming an upper axial cavity between said insert inner
diameter and said shaft outer diameter above said thrust bearing
plate.
Description
BACKGROUND OF THE INVENTION
The following invention relates to hydrodynamic bearings in spindle
motors, and particularly to self-pressure, balanced hydrodynamic
bearings in a spindle motor.
Electric spindle motors of the type used in disk drives
conventionally rely on ball bearings to support a rotary member,
such as a rotating hub, on a stationary member, such as a shaft.
Rolling element or ball bearings are wear parts and, in time,
friction will cause the motor to fail. In addition, ball bearings
create debris in the form of dust or fine particles that can find
their way into "clean" chambers housing the rotary magnetic disks
which are driven by the motor. The mechanical friction inherent in
ball bearings also generates heat and noise, both of which are
undesirable in a disk drive motor.
Hydrodynamic or fluid bearings are often used as a replacement for
ball bearings in disc drives and other apparatus having rotating
parts. In a motor using a fluid bearing, the rotating member is
separated from the stationary member by a film of lubricating
fluid. A fluid bearing offers several advantages over ball bearings
such as low non-repeatable run-out, low audible noise, and high
damping. Also, conventional ball bearings no longer could keep up
with modern high speed motors. Accordingly, fluid bearings
represent a considerable improvement over conventional ball
bearings in spindle drive motors. Examples of fluid bearings
include Titcomb, et al. U.S. Pat. Nos. 5,112,142, 4,795,275 and
5,067,528; Shinohara U.S. Pat. No. 4,445,793; and Anderson, et al.
U.S. Pat. No. 4,726,693.
Two problems plague fluid bearings: the shaft tends to wobble
within the sleeve and lubricating fluid tends to leak from the
motor. If these problems occur the result can be increased wear and
eventual failure of the bearing system or contamination from
lubricating fluid escaping the motor.
Several innovations have been used to reduce the wobbling of the
shaft. For example, a thrust bearing plate incorporated in and
annularly perpendicular to the shaft tends to reduce wobbling. It
should be noted, however, that the primary purpose of a thrust
bearing plate is to support the vertical load, and the reduction of
wobbling is byproduct thereof. Examples of thrust bearing plates
may be found in Hensen U.S. Pat. Nos. 5,433,529 and 5,427,456 which
have been assigned to applicant's assignee and are incorporated
herein by reference. However, because these exemplary thrust
bearing plates are positioned off-center, they only partially
reduce the wobbling. Herringbone grooves cut or coined in the shaft
or the sleeve have also been used to reduce wobbling. Examples of
herringbone grooves may be found in both the aforementioned Hensel
references.
Several innovations have been used to reduce the lubricating fluid
leakage. For example, a labyrinth seal system, as shown in Cheever,
et al. U.S. Pat. No. 5,536,088 which has been assigned to
applicant's assignee and is incorporated herein by reference, tends
to reduce leakage.
Some innovations have been specifically directed to the leakage
caused by changes volume of the lubricating fluid. Changes in
volume may be caused by changes in temperature, among other ways.
Leuthold et al. U.S. Pat. No. 5,524,986 presents the solution of
incorporating a flexible membrane that yields to the increased
pressure of the increasing volume of the fluid. U.S. Pat. No.
5,524,986 attempts to solve this problem by using materials or
combinations of materials such that gaps between the bearing
surfaces become smaller due to different thermal expansion of the
relevant parts. Pan U.S. Pat. No. 5,246,294 uses a large reservoir
with an air cover to store excess lubricating fluid.
Face seals have also been used to reduce leakage. Some examples of
face seals are discussed in "Development of Non-Contacting,
Non-Leaking Spiral Groove Liquid Face Seals" by Tom Lai in the
August, 1994 Journal of the Society of Tribologists and Lubrication
Engineers. The designs discussed therein have significant flaws
such that the author concluded that "a truly non-contacting,
non-leaking seal might not be required for real world
applications."
Despite all the innovations in fluid bearing technology, new and
better technology is still needed to prevent the general problem of
fluid bearings leaking and wobbling.
SUMMARY OF THE INVENTION
The present invention includes several features that alone or in
combination reduce or prevent leakage and wobbling.
More specifically, an embodiment of the spindle motor having
hydrodynamic bearings of the present invention includes a shaft
having a perpendicular radial thrust bearing plate, an insert
surrounding the shaft above the thrust bearing plate to form an
upper axial cavity therebetween, and a sleeve surrounding the shaft
below the thrust bearing plate to form a lower axial cavity
therebetween. In one embodiment the thrust bearing plate is
substantially centrally positioned along the longitudinal axis of
the shaft.
An embodiment of the present invention includes a shaft with
annular skewed herringbone shaft grooves that are preferably skewed
off-center toward the thrust bearing plate. Alternatively, the
insert inner diameter has insert grooves and the sleeve inner
diameter has sleeve grooves. The insert grooves and sleeve grooves
are preferably in an annular skewed herringbone pattern that is
preferably skewed off-center toward the thrust bearing plate. The
upper and lower radial plate surfaces may also have an annular
skewed herringbone pattern that is skewed off-center annularly away
from the shaft. Alternatively, the lower radial insert surface and
the radial sleeve support surface may have an annular skewed
herringbone pattern that is skewed off-center annularly away from
the shaft.
A first set of circulation channels located above the thrust
bearing plate and a second set of circulation channels located
below the thrust bearing plate may be defined in the shaft. Both
sets of circulation channels preferably cross a shaft bore. The
circulation channels and the shaft bore together allow lubricating
fluid to flow in a first direction down from above the thrust
bearing plate to below the thrust bearing plate and to flow in a
second direction up from below the thrust bearing plate to above
the thrust bearing plate. A compensation slot may also be formed in
the insert inner diameter below the upper radial insert
surface.
A face seal may be formed between the lower radial cap surface of
an end cap and an upper radial insert surface of the insert. The
face seal has a face pattern with raised and lowered surfaces on
either the lower radial cap surface or the upper radial insert
surface. The raised surfaces and the opposite surface define a
capillary cavity therebetween. The face pattern, in one embodiment,
has a first annular zone adjacent the shaft, a middle annular
groove, and a second annular zone.
An annular z-slot may be formed below the lower radial cap surface
and between the sleeve inner diameter and the insert outer
diameter.
The foregoing and other objectives, features, and advantages of the
invention will be more readily understood upon consideration of the
following detailed description of the invention, taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side cutaway view of an electronic spindle motor with a
shaft with skewed grooves incorporating several features of the
present invention.
FIG. 2 is a side cutaway view of an alternate electronic spindle
motor with a sleeve and an insert with skewed grooves incorporating
several features of the present invention.
FIG. 3a is a perspective view of a shaft of the present invention
with pressure balance circulation channels.
FIG. 3b is a cross section of the shaft of FIG. 3a taking along
3b--3b.
FIGS. 4a-4b are plan views of alternative thrust grooves of the
present invention.
FIG. 5 is an enlarged view of an upper portion a motor with a
smooth shaft.
FIGS. 6a-6c are plan views of alternative face seals of the present
invention.
FIGS. 7a-7b are enlarged views of the z-slot when the motor is in a
static condition and during rotation, respectively.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows a compact electronic spindle motor 20a. Motor 20a
includes a central shaft 22a, 22b (FIG. 3a) with shaft grooves 23
in its outer diameter 24. Perpendicular to and integral with the
grooved shaft 22a is a radial thrust bearing plate 26 that supports
axial load and provides stability in the axial direction, that is,
along the longitudinal axis of the grooved shaft 22a. The thrust
bearing plate 26 has an upper radial plate surface 28 and a lower
radial plate surface 30. The upper radial plate surface 28 at least
partially supports a smooth insert 31a with a smooth inner diameter
32a. The insert 31a has an upper radial insert surface 33 that
supports an end cap 34 with a lower radial cap surface 35. A smooth
annular sleeve 36a has a smooth inner diameter 38a that partially
encloses the shaft 22a. The sleeve 36a also has a radial sleeve
support surface 40 substantially perpendicular to the sleeve's
inner diameter 38a. The radial sleeve support surface 40 is at
least partially coextensive with the lower radial plate surface
30.
FIGS. 2 and 5 show an alternate embodiment of a compact electronic
spindle motor 20b including a grooved insert 31b and a grooved
sleeve 36b surrounding a smooth central shaft 22b. FIG. 5 shows the
top half of the smooth central shaft 22b with a smooth shaft outer
diameter 24b. Structurally, the bottom half of the smooth shaft 22b
would be identical to the grooved shaft 22a. As shown,
perpendicular to and integral with the smooth shaft 22b would be a
radial thrust bearing plate 26. Further, the thrust bearing plate
26 would have an upper radial plate surface 28 and a lower radial
plate surface 30. The upper radial plate surface 28 at least
partially supports the insert 31b with insert grooves 42 on its
inner diameter 32b. The grooved insert 31b preferably has an upper
radial insert surface 33 that supports an end cap 34 with a lower
radial cap surface 35. An annular sleeve 36b has an inner diameter
38b with sleeve grooves 44 that partially encloses the shaft 22b.
The sleeve 36b also has a radial surface 40 substantially
perpendicular to the sleeve's inner diameter 38b. The radial sleeve
support surface 40 of the sleeve 36b is at least partially
coextensive with the lower radial plate surface 30.
The motor 20a, 20b, when assembled, includes bearing cavities
45a-45d into which lubricant is inserted to form hydrodynamic or
fluid bearings. (Because the smooth shaft 22b is not shown in FIG.
2 the bearing cavities are shown in FIG. 5 and would be identical
to those shown in FIG. 1) An axial insert bearing cavity 45a may be
formed between the inner diameter 32a, 32b of the insert 31a, 31b
and the outer diameter 24 of a shaft 22a, 22b. An axial sleeve
bearing cavity 45b may be formed between the inner diameter 38a,
38b of the sleeve 36a, 36b and the outer diameter 24 of a shaft
22a, 22b. A radial upper bearing cavity 45c may be formed between a
lower radial insert surface 46 of the insert 31a, 31b and the upper
radial plate surface 28 where these surfaces are coextensive. A
radial lower bearing cavity 45d may be formed between the radial
sleeve support surface 40 of the sleeve 36a, 36b and the lower
radial plate surface 30 where these surfaces are coextensive.
Lubricating fluid within the bearing cavities functions as fluid
thrust bearings therein and separates rotating components of the
motor from stationary components of the motor. It should be noted
that the bearing cavities may be tapered to encourage seals to form
such as those disclosed in Charles J. Cheever, et al. U.S. patent
application Ser. No. 08/485,373 which has been assigned to
applicant's assignee and is incorporated herein by reference.
By including both the sleeve 36a, 36b and the insert 31a, 31b in
the motor 20a, 20b, the thrust bearing plate 26 can be positioned
substantially centrally on the longitudinal axis of the shaft 22a,
22b. This centralized position allows a first fluid thrust bearing
to be formed in the radial upper bearing cavity 45c above the
thrust bearing plate 26 and a second fluid thrust bearing to be
formed in the radial upper bearing cavity 45c below the thrust
bearing plate 26. This substantially symmetric configuration tends
to prevent wobbling because it is less likely that the shaft will
become misaligned when the load coincides with the center of
gravity.
As shown in FIGS. 1 and 5 one surface of the bearing cavities 45a,
45b may include herringbone grooves 23, 42, 44 that are skewed so
that the central point 48 of the grooves 23, 42, 44 are off-center
towards the thrust bearing plate 26. By having the grooves 23, 42,
44 skewed towards the center of the shaft 22, net flow of the
lubricating fluid tends to flow towards the center of the motor
20a, 20b and away from the exterior thereof. Graphically, the
pressure would be shaped like a skewed bell curve with the greatest
amount of pressure at the central point 48 and tapering off towards
the end of the bearings. As will be discussed below, as the skewed
grooves 23, 42, 44 generate net flow towards the center of the
motor 20a, 20b, the column of lubricating fluid inside the bearing
cavities 45a, 45b automatically shifts to middle in order to
maintain flow balance. This shifting of the flow creates a pre-load
mechanism that increases overall bearing stiffness.
As shown in FIGS. 4a-4b, one surface of the bearing cavities 45c,
45d may include thrust grooves. FIG. 4a shows outward pumping
thrust grooves 50a and FIG. 4b shows skewed annular herringbone
thrust grooves 50b where the center point of the herringbone 51 is
skewed outward away from the longitudinal axis of the shaft 22a,
22b. Both patterns 50a, 50b cause the pressure distribution created
by the lubricating fluid to move outward and thus stabilize the
shaft 22a, 22b. By moving the pressure distribution outward, there
is a wider base of pressure to support the radial thrust bearing
plate 26 and thus the shaft 22a, 22b tends to be more stable.
Graphically, the pressure distribution of the skewed herringbone
thrust grooves 50b would be shaped like a skewed bell curve with
the greatest amount of pressure at the central point and tapering
off towards the end of the bearings. It should be noted that it
would be undesirable to have lubricating fluid pushed outward if
the thrust bearing plate 26 was located at either end of the shaft,
however, because the thrust bearing plate 26 is substantially
centrally positioned, it is unlikely that the outward pressure will
cause the lubricating fluid to escape the motor 20a, 20b.
FIGS. 1, 3a and 3b, and 5 show a shaft 22a, 22b with two sets of
circulation channels 52. One set 52 is preferably located above the
thrust bearing plate 26 and the other set 52 is preferably located
below the thrust bearing plate 26. Each set 52 crosses a shaft bore
54 that extends at least partially through the axial center of the
shaft 22a, 22b. The circulation channels 52 and the shaft bore 54
together allow lubricating fluid to flow down from above the thrust
bearing plate 26 to below the thrust bearing plate 26. Also, the
circulation channels 52 and the shaft bore 54 together allow
lubricating fluid to flow up from below the thrust bearing plate 26
to above the thrust bearing plate 26. The direction of flow depends
on the difference in the bearing pressure between the axial insert
bearing cavity 45a and the axial sleeve bearing cavity 45b. Thus
when pressure is created by the skewed grooves 23, 42, 44, the
circulation channels 52 and shaft bore 54 allow the motor 20a, 20b
to instantaneously self-pressure balance to reach its balance when
the outside load condition is changed. The circulation channels 52
also store lubricating fluid.
FIGS. 1, 2, and 5 show a compensation slot 60 machined, cut, or
otherwise formed in the insert 31a, 31b. One or more pin hole
access channels 62 (FIG. 5) may optionally be formed in the insert
31a, 31b that allows access to the compensation slot 60 from the
upper radial insert surface 33 once the shaft 22a, 22b and insert
31a, 31b are in place. Accordingly, once the motor 20a, 20b has
been almost completely assembled and filled with lubricating fluid,
a needle or other narrow device may be inserted into the access
channel 62 and a small amount of lubricating fluid may be removed
from the compensation slot 60. By removing lubricating fluid, the
total amount of lubricating fluid is now less than the maximum
amount that can be held in the cumulative volume of the bearing
cavities 45a-45d, circulation channels 52, shaft bore 54, and
compensation slot 60. This empty volume provides the necessary
space to allow the lubricating fluid to migrate upward without
immediately being forced beyond compensation slot 60. The empty
volume also allows lubricating to be exchanged between the axial
insert bearing cavity 45a and the axial sleeve bearing cavity 45b
when pressure inside the cavities is unbalanced. Also, the empty
volume allows the lubricating fluid to expand as it often does when
exposed to environmental and temperature changes. Finally, the
empty volume allows for room for air bubbles.
The centrally positioned thrust bearing plate 26, the two sets of
circulation channels 52, and the compensation slot 60 allow
migration of the lubricating fluid from an initial rest level
(approximately defined at the top by line 64 and at the bottom by
line 65) upward to a rotation level (approximately defined at the
top by line 66 and at the bottom by line 67). When the motor 20a,
20b is in a static condition or at rest, the lubricating fluid
tends to settle downward to the rest level 64, 65. However, when
the motor begins rotating, pressure causes the lubrication fluid to
migrate upward to the rotation level 66, 67. As mentioned above,
during use, as the motor 20a, 20b self-balances itself, the
lubricating fluid automatically adjusts between the rest level 64,
65 and the rotation level 66, 67.
An axial pressure relief groove 63 may be formed between the shaft
22a, 22b and the sleeve 36a, 36b to help reduce pressure on
capillary seals of the motor 20a, 20b.
If the lubricating fluid does escape the compensation slot 60, it
will enter the face seal 70 formed between the upper radial insert
surface 33 of the insert 31a, 31b and the lower radial cap surface
35 of the end cap 34. A similar lower face seal 72 may be formed
between the lower radial sleeve surface 74 of the sleeve 36a, 36b
and a upper radial mounting surface 76 of a mounting structure 78.
One surface of each face seal 70, 72 preferably includes a pattern
80a, 80b, 80c that is coined or otherwise formed therein. The
opposite surface is preferably flat. Each pattern includes raised
(first level) surfaces 82 and lowered (second level) surfaces 84.
The raised surfaces 82 pressing against the flat surface causes a
capillary action trapping lubricating fluid when the motor 20a, 20b
is at rest. This capillary action forms a capillary seal.
Preferably the volume of lubricating fluid that can be held by the
capillary action is equal to or greater than the total volume of
lubricating fluid in the motor 20a, 20b. When the motor 20a, 20b is
rotating, the raised and lowered surfaces 82, 84 of the pattern
80a, 80b, 80c create pressure that pumps the lubricating fluid back
into the gap 86 between the shaft 22a, 22b and the insert 31a,
31b.
The face seal pattern 80a shown in FIG. 6a is a substantially
single zone spiral pattern. A single zone pattern extends
substantially from the shaft 20a, 20b and gap 86 substantially out
to the outer perimeter 87. In a single zone pattern, when the motor
20a, 20b is in a static state, the lubricating fluid tends to
migrate towards the outer perimeter 87. As the object of the seal
is to prevent the lubricating fluid from escaping the seal, this is
undesirable. On the other hand, FIGS. 6b and 6c show patterns 80b
and 80c that are double zone spiral patterns. The first zone 88a
adjacent the shaft is separated from the second zone 88b by a
middle groove 89a. The second zone 88b is separated from the outer
perimeter 87 by an outer groove 89b. In both of these patterns 80b,
80c, the middle groove 89a tends to prevent lubricating fluid from
migrating beyond the first zone 88a. In the rare event that
lubricating fluid migrates into the second zone 88b, the outer
groove 89b prevents the lubricating fluid from escaping to the
perimeter 87. Pattern 80c (FIG. 6c) has larger, more rectangular
raised surfaces 82 that pattern 80b, and therefore tends to allow
less migration than pattern 80b (FIG. 6b). It should be noted that
all three patterns 80a, 80b, and 80c provide both a capillary seal
when the motor 20a, 20b is in a static condition and a dynamic or
pumping seal when the motor 20a, 20b is rotating.
In the rare case that lubricating fluid does escape past the face
seal 70, it may be caught and stored in the z-slots 90. As shown in
FIGS. 1, 2, and 5, the z-slots 90 may be formed between the sleeve
36a, 36b, the insert 31a, 31b, and the end cap 34. The zig-zag
shape of the z-slots 90 is advantageous in that lubricating fluid
flows downward. Because of the force of gravity, lubricating fluid
in the z-slot 90 when the motor is at rest would be positioned as
shown 91a in FIG. 7a. FIG. 7b shows lubricating fluid 91b in the
z-slot 90 when the motor is rotating and the lubricating fluid is
forced downward and outward into the slot by centrifugal force.
An additional capillary seal 92 between the end cap 34 and the
sleeve 36a, 36b may be used as a final deterrent to lubricating
fluid escaping the motor 20a, 20b.
It should be noted that any lubricating fluid such as oil may be
used as a lubricating fluid. Preferably the lubrication fluid
includes antifriction, antiwear, and antioxidant ingredients. In
one embodiment, oil having the approximate viscosity of 30 Cs
(centistrokes) at 20.degree. C. is used, however, alternate fluids
(including gasses and even air) may be used for this purpose.
It should be noted that the grooves 23, 42, 44 include raised
portions called "ridges" with a ridge width and lowered portions
called "grooves" with a groove width. The groove width may be
different from the ridge width as shown. Alternatively, the groove
and ridge widths may have a 1:1 ratio.
It should be noted that the invention may be adapted to work with
spindle motors 20a, 20b having a rotating shaft or stationary shaft
22a, 22b.
Finally, it should be noted that features of the invention may be
incorporated in alternate motors. For example, features such as a
centrally located thrust bearing plate, skewed herringbone grooves,
circulation channels, shaft bores, compensation slots, face seals,
and z-slots may be used in alternative motors. Other features
discussed in the above disclosure can be used alone or in
combination to reduce or prevent leakage and wobbling in
hydrodynamic bearings.
The terms and expressions which have been employed in the foregoing
specification are used therein as terms of description and not of
limitation, and there is no intention, in the use of such terms and
expressions, of excluding equivalents of the features shown and
described or portions thereof, it being recognized that the scope
of the invention is defined and limited only by the claims which
follow.
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